Yielding Spiral Bolt Appendage for a Rock Bolt

ABSTRACT

A yielding spiral holt appendage for attachment to a rock holt has a cylindrical shank portion for attachment to the insertion end or the rock and a helical flute portion having a tip for rupturing a resin cartridge and achieving mixing when rotated. The shank has a first tapered portion and a second tapered portion for resisting movement or the appendage once the resin has set.

TECHNICAL FIELD

This invention relates in general to the held of mining and construction and particularly to ground support equipment and specifically to a yielding spiral bolt appendage for a rock bolt.

BACKGROUND ART

Rock bolting is well known in civil engineering and mining operations. Bolting is done to secure loose rock to stable formations behind. This prevents rock falls and rock bursts which are known to be a major cause of death and injury in the construction and mining industries.

The rock surrounding an excavation subjected to stress fractures into slabs sub-parallel to the tunnel outline. The fracture extend into the surrounding rock to varying depths, expending on such factors as the magnitude and orientation of the stress and the strength of the rock. Dilation occurs during the fracturing process and more significantly, as a result of subsequent stress increases brought about by subsequent mining in the vicinity. The rock bolt is a yielding tendon capable of providing effective support in areas prone to seismic events or high stress changes.

A resin is used to adhere the yielding tendon to the rock. Often the resin is a binary type of adhesive contained in cartridges comprising a bonding agent and a hardening catalyst. Once the capsules are pierced the bonding agent and catalyst mix and the resin begins to set. In operation the resin cartridge(s) is inserted into a predrilled hole that passes through an unstable rock formation into a stable rock formation. A rock bolt is inserted into the drilled hole. The exposed end of the rock bolt that extends outside of the drilled hole is typically equipped with a nut for connection to a rotating device. The insertion end is often tipped with an apparatus to pierce the resin cartridges and mix the resin as the rock bolt is being rotated. It is important to the strength of the bond between the rock bolt, the resin and the rock body that the mixing be thorough. Less than adequate mixing will result in a weakened rock bolt installation.

A number of resin mixing apparatus have been proposed. One such device is shown in U.S. Pat. No. 4,704,052 VERSATILE ROOF BOLT ASSEMBLY issued to Hipkins et al on Nov. 3, 1987. Hipkins discloses an anchor bolt assembly including a helical coil external of and connected to a bolt shall that is coupled to the end of the rock bolt. The tip of the bolt shaft has a frustoconical plug that is used to pierce the resin cartridges as the bolt is rotated to mix the resin. The disadvantage associated with the Hipkins apparatus is that it is a relatively complicated apparatus and hence expensive to manufacture and use in the quantities necessary for rock bolting a major excavation. The Hipkins device comprises a coupler to couple the apparatus to the rock bolt, the helical coil welded to the outside of the apparatus and the frustoconical plus at the head of the apparatus. The coupler itself may present a possible yield point when the assembly is under tension during rock displacement.

Therefore, there is a continued requirement for a mixing apparatus that is easy to manufacture and cost-effective for use in large quantities while providing the necessary mixing results to establish a strong bond between the rock bolt and the rock formation.

DISCLOSURE OF INVENTION Technical Problem Technical Solution

In a preferred embodiment of the invention, there is a spiral bolt appendage for a rock bolt comprising, a body having a shank portion for attachment to the rock bolt integral with a helical flute portion for acting on a resin system placed within a drill hole. In one embodiment of the invention the appendage is threaded onto the end of a rock bolt. In another embodiment the appendage is welded to the end of a rock bolt. In one embodiment of the invention the body is cast from a suitable metal alloy such as hardened steel. In another embodiment of the invention the body is forged. In another embodiment of the invention the helical flute portion may be welded to the shank portion. In one embodiment of the invention the helical flute portion comprises an one-half pitch helix. However, in other embodiments of the invention the helical flute portion may be longer than one-half pitch to suit the installation requirements. The shank portion comprises a bore having a closed end and an open end for receiving an end of the rock bolt. The bore includes a threaded portion for threaded attachment with the end of the rock bolt. The shank portion comprises a cylinder having a first tapered portion and a second tapered portion and an apex between the two tapers. In another embodiment of the invention there is provided a rock bolt comprising a tension member comprising a first end for insertion into a predrilled hole in a rock formation and a second end disposed outside of the predrilled hole having it nut for attachment to a rotating machine. The first end of the rock bolt is threaded to a spiral bolt appendage. In yet another embodiment of the invention there is provided a rock bolting system comprising at least one resin cartridge for placement into a predrilled hole in a rock formation, a rock bolt comprising a tension member having an insertion end having a spiral bolt attached thereto for insertion into the predrilled hole and for piercing the resin cartridge thereby releasing and mixing the resin so that it sets adjacent to the spiral bolt. The tension member exposed end is disposed outside of the predrilled hole for attachment to a rotating machine for rotating the tension member and thereby mixing the resin.

Before explaining one preferred embodiment of the invention in detail, it is to he understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to he understood that the phraseolgy and terminology employed herein are for the purpose of description and should not be regarded as limiting.

ADVANTAGEOUS EFFECTS Description of Drawings

The invention will he better understood and objects or the invention will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

FIG. 1 is a diagram of one preferred embodiment of the invention attached to a rock bolt and installed in a drilled hole.

FIG. 2 comprises a side view of the invention ‘A’, a top view of the invention ‘B’ and a bottom view of the invention ‘C’.

FIG. 3 is a cross-sectional view of the invention along its axis.

FIG. 4 is a perspective view of the invention.

BEST MODE

Referring to FIG. 1, there is shown one embodiment of the invention, a spiral bolt appendage for a rock bolt 10, installed in a drilled hole 2 in order to fix an unstable rock formation 3 to a stable sub-parallel rock formation 4. The invention 10 is attached to the end of a rock holt 5 and embedded in a resin 6 to fix the rock bolt to the rock formation. The appendage may he threaded to the end of the rock bolt as described herein or it may he welded to the end of the thread bolt in alternate embodiments. The portion of the rock holt that extends outside of the drilled hole 2 includes a nut 7 and a hearing plate 8. The nut is tightened against the bearing plate by a rotating device (not shown) to tension the rod. During a yielding event wherein the unstable formation is displaced front the stable formation, tension is placed on the rock bolt until the spiral holt appendage begins to pull out of the hardened resin. In this manner, yielding forces are absorbed by the resin and transmitted to the stable rock formation thereby slowing the yielding event.

Referring now to FIG. 2. there is shown one embodiment of the invention in three views. View ‘A’ is a side view of the invention. view ‘B’ is a top view of the invention and view ‘C’ is a bottom view of the invention. The invention has a length 12, a width 20 and an axis 18 about which is it rotated. The invention comprises a body 10 that is cast from a suitable metal capable of withstanding the forces applied to the body. In one embodiment the metal is a hardened steel alloy. Other alloys are possible. In other embodiments the body can he forged. In a preferred embodiment the body 10 is cast per ASTM 536 grade 120-90-02. The body 10 is comprised of a Fluted section 14 and a cylindrical shank sect ion 16. The flitted section 14 has a top surface 22 having a width 24 that is adequate to pierce resin cartridges placed in a drilled hole. In other embodiments of the invention die fluted section 14 can be welded to the shank portion 16. In the cast or forged embodiment of the body 10 the bottom 30 of the fluted section 14 is integral to the top surface 28 of the shank portion 16. The bottom 32 of the shank portion 16 comprises a bored hole 30 in which the bottom end of the rock bolt is inserted in a threaded arrangement. In another embodiment of the invention, the body is welded to the bottom of the rock bolt.

Still referring to FIG. 2, there is a first taper that is represented by angle 17 that extends from the apex line 38 to the top 28 of the shank 16. There is also a second taper that is represented by angle 19 that extends from apex line 38 to the bottom 32 of the shank 16. In static testing, the tapers have been found to further improve the yielding characteristics of the rock bolt and resin. Referring back to FIG. 1, the tapers are embedded in the resin 6. Taper 17 and taper 10 will resist tensioning forces attempting to push the rock bolt further into the drilled hole or pull the rock bolt out of the drilled hole. The tapers transfer more of the yielding forces to the resin and thereby slow the yielding of the rock bolt.

In a preferred embodiment of the invention the first taper 17 angle is 0.7 degrees and the second taper 19 angle is 1.5 degrees. Other angles can also he used. The length of the body 12 is preferably 3.25 inches with the shank 16 being preferably 2.25 inches long and the fluted portion 14 being one inch long. The width of the shank 16 at end 32 is preferably 0.78 inches and at apex 38 the width of the shank is preferably 0.82 inches. The width 24 of tip 22 is preferably 0.25 inches and the width of the fluted portion at its maximum is 0.78 inches. The flute section 14 comprises a one-half pitch helix and in a preferred embodiment the pitch of the helix is 2 inches. Other dimensions are possible to suit a particular rock bolt installation.

Referring now to FIG. 2 and FIG. 3, there is shown (in FIG. 3) a cross-section along axis 18 one preferred embodiment of the invention 10 comprising the shank portion 16 and the flitted portion 16. The first taper 17 extends along length 39 from apex 38 to the top of the shank portion 28. The second taper 19 extends along length 36 from apex 38 to the end 32 of the shank portion 16. Bore 30 is illustrated as extending from end 32 of the shank substantially to the tip of the shank. The inside surface of the bore 40 is threaded to accept the threaded end of the rock bolt.

Referring now to FIG. 4. there is shown a perspective view of the body 10 comprising the fluted section 14 and the shank portion 16. The first taper extends from apex 38 along length 39 to the top of the shank portion and the second taper extends from apex 38 along length 36 to the bottom 32 of the shank portion. Within bore 30 the inside surface 40 is threaded to mesh with the end of the rock bolt to which the body is attached. In one embodiment of the invention the thread is ¾-10 UNC 2B LH.

It has been found in static testing of the invention that the body of the invention permits effective mixing of the resin within the drill hole so that there is it consistent yield strength of the rock bolt across a sample tested.

It will he appreciate by those skilled in the all that other variations of the embodiments described herein nay also he practiced without departing from the scope of the invention. Other modifications are therefore possible.

MODE FOR INVENTION INDUSTRIAL APPLICABILITY

Sequence List Text 

1. A yielding spiral bolt appendage for attachment to a rock bolt insertion end for placement into a predrilled hole containing a resin system, said spiral bolt appendage comprising a body having a shank portion for attachment to said rock bolt insertion end and a helical tinted portion for acting on said resin system, wherein the resin system comprises an at least one resin cartridge.
 2. The appendage of claim 1 wherein said body is cast so that said shank portion is integral with said helical fluted portion.
 3. The appendage of claim 1 wherein said body is forged.
 4. The appendage of claim 1 wherein the helical fluted portion is welded to the shank portion.
 5. The appendage of claim 1 wherein the helical fluted portion comprises an at least one-half pitch helix and a tip for piercing the at least one resin cartridge and wherein the helical fluted portion is rotated to achieve mixing of the resin within said predrilled hole resulting in set resin around the body.
 6. The appendage of claim 1 wherein the shank portion is cylindrical and comprises a top end, a bottom end and an apex between said top end and said bottom end.
 7. The appendage of claim 6 wherein the shank portion further comprises a first taper from said apex to the shank top end and a second taper from the apex to the shank bottom end.
 8. The appendage of claim 7 wherein said first taper acts on said set resin to resist inward movement of the rock bolt and wherein said second taper acts on the set resin to resist outward movement of the rock bolt.
 9. The appendage of claim 8 wherein the shank further includes a bore having a closed end and an open end for receiving the insertion end of the rock bolt.
 10. The appendage of claim 7 wherein the shank portion is welded to the insertion end of the rock bolt.
 11. The appendage of claim 9 wherein said bore includes in threaded inside surface for threaded attachment with the insertion end of the rock bolt.
 12. A rock bolt assembly comprising a tension member comprising a threaded insertion end for insertion into a predrilled hole into a face of a rock formation and a threaded opposite end exposed out of said predrilled hole, said threaded opposite end having a threaded nut attached thereto and a hearing plate forward of said threaded nut, said threaded nut attachable to a omitting machine for rotation towards said face so that said hearing plate is in contact with the face for tensioning the tension member, wherein said rock bolt assembly further comprises a yielding spiral bolt appendage attached to the insertion end of the rock bolt.
 13. The rock bolt assembly of claim 12 wherein said yielding spiral bolt appendage is threaded onto the insertion end of the rock bolt.
 14. The rock bolt assembly of claim 12 wherein the yielding spiral bolt appendage is welded onto the insertion end of the rock bolt.
 15. The rock bolt assembly of claim 12 wherein the yielding spiral bolt appendage comprises a shank portion having a top end and a bottom end and an apex between said top end and said bottom end and comprising a first taper from said apex to said shank top end and a second taper from the apex to said shank bottom end.
 16. A rock bolting system comprising at least one resin cartridge for placement into a predrilled hole into a face of rock formation a tension member comprising a threaded insertion end for insertion into said predrilled hole and a threaded opposite end exposed out of said predrilled hole, said threaded opposite end having a threaded nut attached thereto and a bearing plate forward of said threaded nut, said threaded nut attachable, to a rotating machine for rotation towards said face so that said bearing plate is in contact with the face for tensioning the tension member, wherein said rock bolt assembly further comprises a yielding spiral bolt appendage for threaded attachment to the insertion end of the rock bolt, wherein said yielding spiral bolt comprises a tip for piercing said resin cartridge and a fluted portion for mixing the resin until the resin sets around the yielding spiral bolt appendage.
 17. The rock bolting system of claim 16 wherein the yielding spiral bolt appendage comprises a shank portion having a top end and a bottom end and an apex between said top end and said bottom end and comprising a first taper from said apex to said shank top end and a second taper from the apex to said shank bottom end.
 18. The rock bolting system of claim 17 wherein said first taper acts on said set resin to resist inward movement cit the rock bolt and wherein said second taper acts on said set resin to resist outward movement of the rock bolt. 